When an aircraft is in flight, air may enter the wing at the leading edge and move along the leading edge cavity (between the front spar and the “D nose” leading edge panel) before exiting the wing at a different location. The movement of air into and out of the wing results in “leakage drag” due to the disruption of airflow over the aerodynamic surfaces of the wing, increasing the overall drag of the aircraft. At high speeds, leakage drag may contribute significantly to the overall drag of the aircraft, reducing performance and increasing fuel consumption.
In order to minimise the leakage drag experienced by an aircraft, it is desirable to reduce or prevent the bulk movement of air along the leading edge cavity. A plurality of transverse ribs present in a conventional aircraft wing structure act to divide the leading edge cavity into a series of compartments, and at least some of these compartments are sealed by the ribs to substantially prevent the movement of air from one compartment to another along the leading edge.
Conventional wing spars typically have a web portion and upper and lower flange portions for attaching to the upper and lower wing covers respectively joined to the web portion. The web portion may be sealed against the ribs and the flange portions may be sealed against the upper and lower wing covers. Gaps may be formed at interfaces between a spar, a rib and a wing cover adjacent a corner between the web portion and one of the flange portions, and these gaps may be sealed using an aerospace grade sealant. A metallic spar may have a relatively sharp corner with a small radius so that the gap is relatively small and easily filled using conventional aerospace sealant.
Modern wing structures may include fibre-reinforced composite spars. Due to the difficulty of forming composite components having an abrupt corner, a composite spar may have a radius corner formed at a junction between a web portion and a flange portion. The radius corner may result in larger gaps being formed adjacent the outside of the radius corner where the spar meets a wing panel and a rib than would be experienced with a conventional metallic spar having a corner with a smaller radius. These gaps may be difficult to satisfactorily seal using conventional aerospace sealant due to the dimensions of the gaps.